Extant holocephalans are an anatomically bizarre group of deep sea dwelling fishes which are highly adapted to durophagy, and extraordinarily slow-evolving. They are also the tip of a lineage which has survived three big mass-extinctions. Thus, holocephalans have great potential as a case study in how evolution shapes morphology in response to selection pressures over vast periods of time, and how this morphology is affected by mass extinction events. We will bring together new collaborations to investigate the relationship between the form of the holocephalan skull and jaws and their function in durophagy. We will take a novel approach based around three objectives: functional morphology, ontogeny, and paleontology. The methods we will use have never been applied to this question before. We expect this project to lay the groundwork for future collaboration between our teams, as well as helping to develop the application of similar modelling methods to other fields of paleontology.